The magnetic resonance imaging provides images such as those of plane sections of a body, by making use of the property of a certain atom or nucleus (such as a hydrogen atom or nucleus) which exhibits a magnetic resonance phenomenon when it is placed in a uniform static magnetic field, causing its spin to have a precession about the static magnetic field, and when a radio frequency pulse (RF pulse) having the same frequency as that of the precession is applied to the body in that state. Magnetic resonance imaging employing the Fourier transform technique superimposes gradient magnetic fields G.sub.x, G.sub.y, and G.sub.z over the static magnetic field, the gradient magnetic fields having their strengths varying along the three axes consisting of the X axis, Y axis and Z axis. This allows each individual atom or nucleus in an object to undergo a magnetic resonance or relaxation with the frequency that varies with the varying strengths of the magnetic fields G.sub.x, G.sub.y, G.sub.z. The frequency of the echo signal that results from the magnetic resonance or relaxation is then analyzed by employing the Fourier transform, and an image is provided.
The typical pulse sequence which may be used in the magnetic resonance imaging that employs the Fourier transform is presented in FIG. 1. As can be seen from FIG. 1, the 9020 RF pulse 11 whose amplitude is maodulated with a 21-MFz carrier, and the gradient magnetic field G.sub.z 13 along the Z axis are intended to enable a selective excitation of the plane sections which are perpendicular to the Z axis. The 180.degree. RF pulse 12 and the gradient magnetic field G.sub.x 14 along the X axis are intended to provide a signal that results from the excited spin in the form of an echo signal 16. The echo signal 16 at that point in time contains a frequency component which depends upon the distribution of the spin along the X axis within a particular plane section, and this distribution of the spin along the X axis is encoded in the form of the frequency of the echo signal (frequency encoding). Moreover, the gradient magnetic field G.sub.y 15 which extends along the Y axis orthogonally to each of the two gradient magnetic fields G.sub.z and G.sub.x has its magnitude value shifted from the positive to negative (or vice versa) sequentially each time one echo signal (view) is collected. This causes the amount of the phase encoding to change accordingly which allows the distribution of the spin along the Y axis within the plane section to be encoded in the form of the phase of the echo signal (phase encoding).
The described magnetic resonance imaging that employs t he Fourier transform is currently available in various types, some of which are named as follows: